[issue23185] add inf and nan to math module
STINNER Victor added the comment: Guido van Rossum added the comment: Should inf and nan be added to cmath too? It has e and pi and isnan() and isinf()... Also complex(0, math.nan) a value that is printed as nanj and complex(nanj) parses and returns such a value, so the point could be made that there should be a constant named complex.nanj. Since it's a different module and we are talking about more and different constants, I suggest to open a new issue. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Mark Dickinson added the comment: Opened issue #23229. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Mark Dickinson added the comment: Should inf and nan be added to cmath too? Hmm; probably, yes. I'll open an issue. so the point could be made that there should be a constant named complex.nanj Yes, I suppose it could (along with infj, of course). I don't like it much, and I suspect it would get almost no uses. complex(0, inf) and complex(0, nan) seem like good enough spellings. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Guido van Rossum added the comment: Should inf and nan be added to cmath too? It has e and pi and isnan() and isinf()... Also complex(0, math.nan) a value that is printed as nanj and complex(nanj) parses and returns such a value, so the point could be made that there should be a constant named complex.nanj. -- nosy: +gvanrossum ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Mark Dickinson added the comment: Committed. Thanks for all the helpful review comments! -- resolution: - fixed stage: needs patch - resolved status: open - closed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Roundup Robot added the comment: New changeset cf4bf577749c by Mark Dickinson in branch 'default': Issue #23185: add math.inf and math.nan constants. https://hg.python.org/cpython/rev/cf4bf577749c -- nosy: +python-dev ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Changes by Ethan Furman et...@stoneleaf.us: -- nosy: +eric.smith, lemburg, rhettinger, stutzbach ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
STINNER Victor added the comment: 2015-01-09 8:16 GMT+01:00 Serhiy Storchaka rep...@bugs.python.org: May be make math.inf and math.nan special objects so that for all x (except inf and nan): What do you mean? Implement a subtype of float and override some methods? x math.inf x -math.inf It's already the case for int, float and decimal.Decimal. not (x math.nan) not (x math.nan) Comparison to nan always return False. I would be better to raise an error when nan is compared to other numbers (I mean operations like ab, not a==b), but Python was not designed like that (nor the IEEE 754?). sorted((nan, 1, nan, 2)) [nan, 1, nan, 2] Sorting with NaN is a common issue :-/ See for example: https://stackoverflow.com/questions/4240050/python-sort-function-breaks-in-the-presence-of-nan Anyway, changing NaN behaviour is out of the scope of this issue! -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Serhiy Storchaka added the comment: May be make math.inf and math.nan special objects so that for all x (except inf and nan): x math.inf x -math.inf not (x math.nan) not (x math.nan) -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
STINNER Victor added the comment: Except of my small suggestion on the doc (see the review), math_inf_nan4.patch looks good to me. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Mark Dickinson added the comment: I have an updated patch taking into account the most recent review comments (for which thanks!), but it's at home; I'll upload it this evening (UTC+00:00). -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Mark Dickinson added the comment: New patch, addressing review comments. -- Added file: http://bugs.python.org/file37647/math_inf_nan4.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Mark Dickinson added the comment: One more patch, fixing a misplaced period. -- Added file: http://bugs.python.org/file37635/math_inf_nan3.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
STINNER Victor added the comment: History, perhaps? In any case, the sign of a NaN isn't useful information in the same way that the sign of an infinity is. The IEEE 754 standard explicitly refuses to attach any meaning to the sign bit of a NaN. And if we were aiming for a full and faithful representation of NaNs, we'd want to output the payload, too (which is just about as meaningless / meaningful as the sign bit). So I understand that adding a math.neg_nan would be useless. As adding one constant per possible NaN value :-) If I recall correctly the IEEE 754 standard, there is not single NaN value, but a range of NaN. Two kinds of NaN: a quiet NaN (qNaN) and a signaling NaN (sNaN). A NaN may carry a payload that is intended for diagnostic information indicating the source of the NaN. The sign of a NaN has no meaning, but it may be predictable in some circumstances. says Wikipedia. Well, the current definition of math.nan makes sense, it's the same value than float(nan). Note: On python-ideas, I asked if math.nan and math.inf should be singleton (as it was requested for float(0.0) in issue #4024). The answer is no. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Changes by Berker Peksag berker.pek...@gmail.com: -- components: +Library (Lib) stage: - needs patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Mark Dickinson added the comment: Sounds good to me. Do we add a math.neginf IMO no: -inf should be fine. -- nosy: +mark.dickinson ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Mark Dickinson added the comment: float(-inf) and -float(inf) have exactly the same IEEE 754 representation Indeed: there's only one negative infinity (and only one positive infinity) in IEEE 754 binary64 format. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Mark Dickinson added the comment: Implementation suggestion: if possible, use the _Py_dg_stdnan and _Py_dg_infinity functions from Python/dtoa.c. These are a little safer than the Py_NAN and Py_HUGE_VAL macros, and will give results consistent with the float(inf) and float(nan) constructions. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
New submission from Ethan Furman:
Proposal:
math.nan = float('nan')
math.inf = float('inf')
Guido's approval:
https://mail.python.org/pipermail/python-ideas/2015-January/030775.html
Followup question:
Do we add a math.neginf, or somesuch, for float('-inf')? Or just use
-math.inf?
--
keywords: easy
messages: 233580
nosy: ethan.furman
priority: normal
severity: normal
status: open
title: add inf and nan to math module
type: enhancement
versions: Python 3.5
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[issue23185] add inf and nan to math module
STINNER Victor added the comment:
Do we add a math.neginf, or somesuch, for float('-inf')? Or just use
-math.inf?
I would prefer to only add inf.
It looks like float(-inf) and -float(inf) have exactly the same IEEE 754
representation (at least on my x86_64 CPU):
struct.pack(d, float(-inf)) == struct.pack(d, -float(inf))
True
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nosy: +haypo
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[issue23185] add inf and nan to math module
Mark Dickinson added the comment: Why does Python return the same representation for positive and negative NaN? History, perhaps? In any case, the sign of a NaN isn't useful information in the same way that the sign of an infinity is. The IEEE 754 standard explicitly refuses to attach any meaning to the sign bit of a NaN. And if we were aiming for a full and faithful representation of NaNs, we'd want to output the payload, too (which is just about as meaningless / meaningful as the sign bit). -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Serhiy Storchaka added the comment:
There are several different NaNs.
x = struct.unpack('d', b'\x00\x00\x00\x00\x00\x00\xf8\x7f')[0]
x
nan
x == x
False
struct.pack('d', x)
b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
x = struct.unpack('d', b'\x00\x00\x00\x00\x00\x00\xf9\x7f')[0]
x
nan
x == x
False
struct.pack('d', x)
b'\x00\x00\x00\x00\x00\x00\xf9\x7f'
Interesting, but 0*inf and inf-inf return values with the same representation
as float('-nan'), not float('nan').
inf = float(inf)
struct.pack('d', 0*inf)
b'\x00\x00\x00\x00\x00\x00\xf8\xff'
struct.pack('d', inf-inf)
b'\x00\x00\x00\x00\x00\x00\xf8\xff'
struct.pack('d', float('nan'))
b'\x00\x00\x00\x00\x00\x00\xf8\x7f'
struct.pack('d', float('-nan'))
b'\x00\x00\x00\x00\x00\x00\xf8\xff'
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[issue23185] add inf and nan to math module
Mark Dickinson added the comment:
but 0*inf and inf-inf return values with the same representation as
float('-nan'), not float('nan')
Right: that's because Intel's default NaN (i.e., the float it produces as a
result of any invalid operation) has its sign bit set.
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[issue23185] add inf and nan to math module
Mark Dickinson added the comment: By tweaking the grammar we can have math.-inf. RRGH! -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Antoine Pitrou added the comment: By tweaking the grammar we can have math.-inf. -- nosy: +pitrou ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Mark Dickinson added the comment: Here's a patch. -- assignee: - mark.dickinson keywords: +patch Added file: http://bugs.python.org/file37633/math_inf_nan.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
Mark Dickinson added the comment: Thanks for the review comments. Here's an updated patch taking the review comments into account (and fixing the spelling of PY_NAN, which should have been Py_NAN). -- Added file: http://bugs.python.org/file37634/math_inf_nan2.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue23185] add inf and nan to math module
STINNER Victor added the comment: Oh, NaN can be signed? struct.pack(d, float(nan)) b'\x00\x00\x00\x00\x00\x00\xf8\x7f' struct.pack(d, float(-nan)) b'\x00\x00\x00\x00\x00\x00\xf8\xff' struct.pack(d, -float(nan)) b'\x00\x00\x00\x00\x00\x00\xf8\xff' struct.pack(d, -float(-nan)) b'\x00\x00\x00\x00\x00\x00\xf8\x7f' Why does Python return the same representation for positive and negative NaN? float(nan) nan float(-nan) nan -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue23185 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
